Condensation polymer containing hydroxyalkylamide groups

ABSTRACT

The invention relates to a linear or branched polymer containing ester groups and at least one amidegroup in the backbone, having hydroxyalkylamide end groups and having a weight average molecular mass of ≧800 g/mol. The invention also relates to an entirely or partly modified polymer. The polymer according to the invention can for example be obtained by reaction of a cyclic anhydride and an alkanolamine to form a β-hydroxyalkylamide, after which a polyesteramide is obtained through polycondensation. The polymers according to the invention can, for example, be used in thermosetting powder-paint compositions.

This is a continuation of International Appln. No. PCT/NL98/00546 filedSep. 22, 1998 which designated the U.S.

The invention relates to a linear or branched condensation polymercontaining ester groups and at least one amide group in the backbone,having at least one hydroxyalkylamide endgroup and having a weightaverage molecular mass of ≧800 g/mol.

Preferably, the polymer contains at least two groups according toformula (I)

in which

or (C₆-C₁₀) aryl,

B=(C₂-C₂₄), optionally substituted, aryl or (cyclo)alkyl aliphaticdiradical,

R¹, R², R³, R⁴, R⁵ and R⁶ may, independently of one another, be the sameor different, H, (C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical and

n=1-4.

More preferably the polymer contains at least two groups according toformula (II):

in which

or (C₆-C₁₀) aryl,

B=(C₂-C₂₄), optionally substituted, aryl or (cyclo)alkyl aliphaticdiradical, and

R¹, R², R³, R⁴, R⁵ and R⁶ may, independently of one another, be the sameor different, H, (C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical.

According to a further preferred embodiment, the polymer containinghydroxyalkylamide groups is a polymer according to formula (III):

in which:

or (C₆-C₁₀)aryl

B=(C₂-C₂₄), optionally substituted, aryl or (cyclo)alkyl aliphaticdiradical,

X²=H or X¹ and

R¹, R², R³, R⁴, R⁵ and R⁶ may, independently of one another, be the sameor different, H, (C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical orCH₂—OX².

In formulas (I), (II) and (III) R groups may together or withneighbouring carbon atoms form part of a cycloalkyl group.

According to another preferred embodiment of the invention, the polymercontaining β-hydroxyalkylamide groups is a polymer according to formula(IV):

in which:

(C₆-C₁₀)aryl,

B=(C₂-C₂₀), optionally substituted, aryl or (cyclo)alkyl aliphaticdiradical,

X²=H or X¹,

R³=H or (C₆-C₁₀) aryl or (C₁-C₈)alkyl radical and

R⁶=H or (C₆-C₁₀) aryl or (C₁-C₈)alkyl radical.

The weight average molecular mass of the polymer according to theinvention is generally between 800 and 50,000, and preferably between1000 g/mol and 25,000 g/mol.

The number average molecular mass is generally between 600 and 10,000and preferably between 700 and 4000.

The hydroxyalkylamide functionality is generally between 2 and 250 andpreferably between 5 and 50.

Functionality is the average number of reactive groups of the specifictype per molecule in the polymer composition.

According to another preferred embodiment of the invention the polymer'shydroxyalkylamide functionality of the polymer is ≧5 and the polymercontaining β-hydroxyalkylamide groups is a polymer represented byformula (V):

in which:

B=(C₂-C₁₂), optionally substituted, aryl or (cyclo)alkyl aliphaticdiradical,

X²=H or X¹,

R³=H or (C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical and

R⁶=H or (C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical

Preferably R³ and R⁶ are (C₁-C₄) alkyl.

According to another preferred embodiment of the invention R³ and R⁶ aremethyl or ethyl.

B may be saturated or unsaturated.

B may be substituted with for example a (C₁-C₂₆) alkyl group, which maybe saturated or unsaturated; preferably C₁ is used.

B may be for example a (methyl-)1,2-ethylene, (methyl-)1,2-ethylidene,1,3-propylene, (methyl-)1,2-cyclohexyl, (methyl-)1,2-phenylene,1,3-phenylene, 1,4-phenylene, 2,3-norbornyl, 2,3-norbornen-5-yl and/or(methyl-)1,2 cyclohex-4-enyl radical.

Depending on the starting monomers chosen, the variables B, R¹, R², R³,R⁴, R⁵ and R⁶ in the molecule or mixture of molecules can be selected tobe the same or different per variable.

The polymer composition according to the invention is generally acomposition comprising higher and lower oligomers, which usuallycontains less than 50 wt. %, preferably less than 30 wt. %, of oligomershaving a molecular weight smaller than 600.

The polyesteramide according to the invention can for example beobtained through polycondensation of mono- and/or bis-hydroxyalkylamidesof bivalent carboxylic acids.

The monohydroxyalkylamide of a bivalent carboxylic acid generally hasthe formula (VI):

and the bishydroxyalkylamide of a bivalent carboxylic acid generally canbe represented by formula (VII):

wherein

R¹, R², R³ and R⁴ may, independently of one another, be the same ordifferent, H, (C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical.

Consequently a lineair polymer according to the invention generallycomprises the amide and the ester groups alternating along the chain asfollows:

E-A-E-A-A-E-A-E-A-E

wherein a diamide is coupled with alternating ester (E)-amide (A)groups.

A branched polymer according to the invention generally comprises theamide and the ester groups alternating along the main and side chains asfollows:

wherein a diamide is coupled with alternating ester (E)-amide (A)groups.

In the branched polymers according to the invention(β)-hydroxyalkylamide groups can be present both as an endgroup

and as a pendant side chain group

Generally, the molar amount of amide bounds in the chain is higher thanthe amount of ester bounds.

The polymer according to the invention comprises at least 60% by weightof the products represented by the formulas (III)-(V).

Due to side reactions during the preparation of the polymer it ispossible that the composition according to the invention comprises alsofor example secundary amine groups having the formula (VIII):

wherein:

R¹, R², R³ and R⁴ may, independently of one another, be the same ordifferent, H, (C₆-C₁₀) aryl or (C₁-C₈) (cyclo)alkyl radical.

The polymer according to the invention can, also be obtained in aone-step procedure by reacting a cyclic anhydride and an alkanolamine,at a temperature between for example about 20° C. and about 100° C., toform a hydroxyalkylamide, after which, at a temperature between, forexample, 120° C. and 250° C., a polyesteramide is obtained throughpolycondensation with water being removed through distillation.

The reaction can take place without a solvent, but also in water or inan organic solvent.

The removal of water through distillation can take place at a pressurehigher than 1 bar, in a vacuum or azeotropically.

Preferably, the cyclic anhydride is an anhydride according to formula(IX):

in which B has the meaning specified above.

Examples of suitable cyclic anhydrides include phthalic anhydride,tetrahydrophthalic anhydride, naphtalenic dicarboxylic anhydride,hexahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride,norbornene-2,3-dicarboxylic anhydride, naphtalenic dicarboxylicanhydride, 2-dodecene-1-yl-succinic anhydride, maleic anhydride,(methyl)succinic anhydride, glutaric anhydride, 4-methylphthalicanhydride, 4-methylhexahydrophthalic anhydride,4-methyltetrahydrophthalic anhydride and the maleinised alkylester of anunsaturated fatty acid.

Preferably the alkanol is an alkanolamine according to formula (X):

in which:

R¹, R², R³, R⁴, R⁵ and R⁶ may, independently of one another, be the sameor different, H, (C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical or CH₂OHand n=1-4.

More preferably n=1. The alkanolamine may be a monoalkanolamine, adialkanolamine, a trialkanolamine or a mixture hereof.

If monoalkanolamines are used in one of the possible polymer syntheses,linear polymers with a functionality of 2 can be obtained. Depending onthe application desired, a linear or an entirely or partly branchedpolymer can be chosen, in which case the degree of branching can be setvia the alkanolamines chosen.

If a highly branched structure with a high functionality is desired, di-or trialkanolamines are used as the starting compound.

Examples of suitable mono-β-alkanolamines include ethanolamine,1-(m)ethyl ethanolamine, n-butyl ethanolamine, 1-(m)ethylisopropanolamine, isobutanolamine, β-cyclohexanolamine, n-butylisopropanolamine and n-propanolamine.

Examples of suitable di-β-alkanolamines are 3-amino-1,2-propanediol,2-amino-1,3-propanediol diisobutanolamine (bis-2-hydroxy-1-butyl)amine),di-β-cyclohexanolamine and diisopropanolamine(bis-2-hydroxy-1-propyl)amine).

A suitable trialkanolamine is, for example,tris(hydroxymethyl)aminomethane.

Preferably a β-alkyl-substituted β-hydroxyalkylamide is used. Examplesare (di)isopropanolamine, cyclohexyl isopropanolamine, 1-(m)ethylisopropanolamine, (di) isobutanolamine, di-β-cyclohexanolamine and/orn-butyl isopropanolamine.

This results in polymer compositions with improved resistance tohydrolysis.

Most preferable are diisopropanolamine and diisobutanolamine.

The anhydride:alkanolamine equivalent ratio is generally between 1.0:1.0and 1.0:1.8. Preferably, this ratio is between 1:1.05 and 1:1.5.

The compound according to the invention can also be obtained via areaction between an alkanolamine, as for example described above, and acompound containing one acid group and one activated acid group, afterwhich a polyesteramide is obtained through polycondensation.

The compound containing an acid group and an activated acid group ispreferably a compound according to formula (XI):

in which

B has the meaning specified above and

in which R⁷ is a (C₁-C₁₂) branched or linear alkyl group.

Examples of suitable compounds containing one acid group and oneactivated acid group are alkyl esters, such as, for example,mono(m)ethyl adipate and mono(m)ethyl sebacate, anhydrides andthioesters.

The compound according to the invention can also be obtained via areaction between a cyclic anhydride, as for example described above, andan alcohol, after which the reaction product obtained reacts in situwith an alkanolamine and a polyesteramide is subsequently obtainedthrough polycondensation.

Examples of suitable alcohols are (C₁-C₁₀) alcohols.

Preferably, methanol or ethanol is used.

In addition to hydroxyalkylamide groups, the polymer may also containcarboxyl groups, in amounts of between 0.01 and 2.0 mg equivalent/gramof polymer. The number of carboxylic acids present in the polymer can becontrolled via the anhydride/alkanolamine ratio and via the degree ofconversion. If an alkanolamine excess is used and thepolycondensationreaction is (almost) complete, less than 0.2 mgequivalent acid/gram of polymer is usually present. If carboxyl groupsare present, they may in a subsequent step react with compoundscontaining one or more groups that can react with carboxylic acid, suchas for example epoxy groups or β-hydroxyalkylamide groups. The amount ofcarboxylic acid is preferably as low as possible, for example between0.01 and 0.2 mg equivalent/gram of polymer.

The degree of branching and the functionality of the polymer aredependent on the starting materials and the molecular weight of thepolymer. A molecular weight higher than 2000 and the use of di- and/ortrialkanolamines generally lead to highly branched structures with afunctionality of ≧10.

Due to the presence in amounts of less than 10% by weight (of the totalamount of anhydrides) of bis- and dianhydrides instead of the anhydridesaccording to formula (IX) it is possible that the polymer does notcomprise only products according to formulas (III)-(V).

The invention also relates to entirely or partly modified polymers.

The modification can for example take place via a reaction between thepolymer according to any one of formulas (III), (IV) or (V) with amonomer, oligomer or polymer containing reactive groups that can reactwith the hydroxyalkylamide.

Examples of suitable reactive groups include carboxyl groups, carboxylicesters, carboxylic anhydrides, epoxy groups, alkoxysilane groups,isocyanate groups, acid chloride groups, epoxychlorohydrine groups,amine groups, phenolic groups, methylolated amidegroups and combinationshereof.

Preferably the monomer, oligomer or polymer contains only one group thatcan react with hydroxylalkylamide, as a result of which no crosslinkingtakes place during the modification.

The polymer according to formula (III), (IV) or (V) has preferably beenmodified with a compound containing a carboxylic acid group.

A modified polymer can for example be represented by one of the formulas(III), (IV) or (V) in which

and

in which

is derived from a monomeric, oligomeric or polymeric monofunctionalcarboxylic acid.

Suitable carboxylic acids are, for example, saturated aliphatic (C₁-C₂₆)acids, unsaturated (C₁-C₂₀) fatty acids, aromatic acids and α,β-unsaturated acids.

Examples of suitable α,β-unsaturated acids are (meth)acrylic acid,crotonic acid and monoesters or monoamides of itaconic acid, maleicacid, 12-hydroxystearic acid, polyether carboxylic acid, and fumaricacid.

Suitable saturated aliphatic acids are for example acetic acid,propionic acid, butyric acid, 2-ethyl hexanoic acid, laurylic acid andstearic acid.

Suitable aromatic acid are for example benzoic acid and tertiairy butylbenzoic acid.

Z can be chosen from, for example, a saturated or unsaturated (C₁-C₄₀)alkyl or aromatic group, a polymer or an oligomer. Examples of suitablepolymers are polyesters, polyethers and poly(capro)lactones.

Z can be substituted with for example ester groups, ether groups, amidegroups and alcohol groups.

The modified polymer may consist of the same or different Z groups.

The branched polymer according to the invention can also react with adiisocyanate, after which the isocyanate-functional polymer obtainedreacts with a compound capable of reacting with isocyanates. As thediisocyanate use is preferably made of a compound containing two or moreisocyanate groups with different reactivities. This is preferably analiphatic diisocyanate with one sterically more accessible isocyanategroup bound to a primary carbon atom and one sterically less accessibleisocyanate group bound to a tertiary carbon atom.

Examples of suitable diisocyanates are1,4-diisocyanato-4-methyl-pentane, 1,5-diisocyanato-5-methylhexane, 3(4)-isocyanatomethyl-1-methylcyclohexylisocyanate,1,6-diisocyanato-6-methylheptane, 1,5-diisocyanato-2,2,5-trimethylhexaneand 1,7-diisocyanato-3,7-dimethyloctane, and1-isocyanato-1-methyl-4-(4-isocyanatobut-2-yl) -cyclohexane,1-isocyanato-1,2,2-trimethyl-3-(2-isocyanato-ethyl)-cyclopentane,1-isocyanato-1,4-dimethyl-4-isocyanatomethyl-cyclohexane,1-isocyanato-1,3-dimethyl-3-isocyanatomethyl-cyclohexane,1-isocyanatol-n-butyl-3-(4-isocyanatobut-1-yl)-cyclopentane and1-isocyanato-1,2-dimethyl-3-ethyl-3-isocyanatomethyl-cyclopentane,respectively.

The preferred isocyanates are3(4)-isocyanato-methyl-1-methylcyclohexylisocyanate (IMCI) andisophorone diisocyanate.

Monomers, oligomers and polymers can all be used as the compounds thatcan react with isocyanate groups. Such compounds contain reactive groupsthat can form a chemical bond with isocyanate groups.

Examples of suitable reactive groups are alcohols and amine groups.

Examples of suitable compounds are hydroxyethyl(meth)acrylate,hydroxy(C₂-C₁₂)alkyl vinyl ether, 4-hydroxybutyl(meth)acrylate,aminopropyl vinyl ethers, aminoalkyl vinyl ether,aminopropyl-tri(m)ethoxysilane and aminoalkyltrialkoxysilane.

Preferably the diisocyanate, for example IMCI, is combined with aselective catalyst, as a result of which no chain lengthening orcrosslinking will take place.

As the catalyst use can be made of an ionogenic metal complex based on ametallic element from any one of groups III, IV or VII of the PeriodicSystem with exchangeable counterions. Examples of suitable catalysts aretitanium (IV) butoxide, zirconium (IV) acetylacetonate, zirconium (IV)butoxide, tin (IV) acetate, manganese (III) acetylacetonate, titanium(IV) isopropoxide, zirconium (IV) 2-ethylhexanoate and tin (IV)chloride.

The modified and the unmodified polymers can be very widely used intechnically different fields, both in thermosetting and in thermoplasticapplications. Examples are powder-paint compositions, coating systemsbased on water or solvent, can- or coil-coating systems,radiation-curable coating compositions, alkyd resins for coatings,unsaturated resins for construction purposes (for example putties,sealants, castings, compounds and molding compounds), inks, toner , filmformers for glass fibre sizings, adhesives, hot melts and in rubbercompositions.

Unmodified or partly modified polymers according to the invention willgenerally be used in powder-paint systems, in can- or coil-coatingsystems or in solvent-based coating systems.

If the modification has been realized with the aid of for example fattyacids, the polymers according to the invention can be used as airdryingsystems.

A modification with radically curable compounds offers possibilities inthe technical fields of radiation-curable coatings and constructionresins.

Considering the many possibilities of modification of the polymeraccording to the invention, modification can be directed at any of awide range of technical applications.

The polymers according to the invention can be used in thermosettingpowder-paint compositions. Preferably use is made of the polymerscontaining β-hydroxyalkylamide groups.

Thermosetting powder paints have a better resistance to chemicals thanthermoplastic powder paints. As a result of this, intensive efforts havefor a long time been made to develop crosslinkers and polymers forthermosetting powder coatings. Attempts are still being made to findbinder compositions for thermosetting powder paints with a good flowbehaviour, good storage stability and a good reactivity. A thermosettingpowder-paint binder composition generally contains more than 50 wt. %polymer and less than 50 wt. % crosslinker.

The polymer according to the invention can be used in a powder-paintcomposition as a polymer and as a crosslinker.

The glass transition temperature (Tg) of the polymer according to theinvention lies between 0° C. and 150° C., preferably between 50° C. and110° C., depending on the selected starting materials and the molecularweight.

Preferably a compound according to any one of formulas (I), (II), (III),(IV) or (V) is used in powder-paint compositions. It is also possible touse a polymer in which up to for example 50 wt. %, preferably less than30 wt. %, of the hydroxyalkylamide groups are modified.

A coating that ultimately obtained with a powder paint must meet manyvarying requirements. Various systems are known. Some systems releasevolatile components during the curing. These systems present thedrawback that they form coatings with bubbles and/or that undesirableemissions are released. As far as the latter is concerned, the volatilecomponent, if organic in origin, may cause undesirable environmental orhealth problems. It has moreover been found that all the desiredproperties of the powder paint or powder coating are not alwaysrealized.

Systems comprising hydroxyalkylamide crosslinkers, such as for exampleaccording to EP-A-322834, contain bubbles above a layer thickness limitof about 100 μm as a result of the reaction water released.

In other systems use is made of polyesters and the usual crosslinkerscontaining an epoxy group. No volatile components are generally releasedfrom these systems. However, the use of bisphenol-A-epoxy resins in theso-called hybrid systems results in coatings that exhibit a relativelygreat extent of yellowing and powdering when exposed to UV light, whilethe frequently used triglycidylisocyanurate (TGIC) crosslinker istoxicologically suspect.

It has been found that use of the polymer according to the invention asthe crosslinker in binder compositions for powder paints results in acombination of highly desirable properties such as for instance goodflow behaviour and good resistance to chemicals, desired gloss withoutbubble formation at the surface up to and including layer thicknesses ofat least 120 μm, a high resistance to scratching, good mechanicalproperties, good powder stability, good weather resistance and goodcolour stability of the powder coating.

It is surprising that use of the highly functional crosslinkersaccording to the invention leads to good flow behaviour, becausegenerally a crosslinker having a functionality higher than, for example,6 results in reduced flow behaviour.

Depending on the final application desired, the crosslinker according tothe invention described above can also be used in combination withanother crosslinker, such as for example triglycidyl isocyanurate(TGIC), polybisphenol-A-epoxides such as, for instance, the variousEpikote™ grades, compounds containing (blocked) isocyanate groups, suchas for example the caprolactam-blocked isophorone diisocyanate trimer,crosslinkers containing β-hydroxyalkylamide groups such as for examplePrimid XL 522™ (Rohm and Haas) and/or polyfunctional oxazolines. Theweight ratio between the crosslinkers can be selected depending on thefinal application.

The crosslinker according to the invention is preferably combined with acrosslinker comprising at least one linear or branched aliphatic chainwith 5-26 carbon atoms and having an epoxy functionality of more than 1,with the proviso that the epoxy groups are carried on the at least onealiphatic chain. These crosslinkers are described in EP-A-600546 andinclude, for example, epoxidized oils in which the oil is linseed oil,soybean oil, safflower oil, oiticica oil, carraway seed oil, rapeseedoil, castor oil, dehydrated castor oil, cottonseed oil, wood oil,vernonia oil (a natural oil), sunflower oil, peanut oil, olive oil,soyleaf oil, maize oil, fish oil such as, for instance, herring orsardine oil, and non-cyclic terpene oils.

The epoxidized oil is preferably epoxidized soybean oil and/orepoxidized linseed oil.

As the crosslinker, a powder-paint-binder composition may contain thepolymer according to the invention and as the polymer a polymercontaining carboxyl groups or containing anhydride groups.

A polyester, a polyacrylate, a polyether (such for example a polyetherbased on bisphenol or a phenol-aldehyde novolak), a polyurethane, apolycarbonate, a trifluoroethylene copolymer or a pentafluoropropylenecopolymer, a polybutadiene, a polystyrene or a styrene maleic anhydridecopolymer can for example be chosen as the polymer.

Generally, polymers having an acid value higher than 40 mg KOH/gramresins are applied because a relatively high acid value results inbetter reactivity with the polymer according to the invention.

The molecular weight (Mn) of this polymer is usually higher than 800,but preferably higher than 1500. The polymer must flow well attemperatures between 100° C. and 200° C. and therefore has a molecularweight (Mn) that is lower than approximately 10,000, preferably lowerthan approximately 7000.

This polymer generally has a viscosity at 158° C. that is lower than8000 dPas. The viscosity will usually be higher than 100 dPas. Theviscosity can advantageously vary from approximately 300 toapproximately 5000 dPas. The viscosity used here was measured accordingto the Emila method described by Misev in Powder Coatings; Chemistry andTechnology, pages 287-288 (1991).

The Tg of this polymer is generally higher than approximately 20° C.,preferably higher than 30° C., and may be higher than 40° C. Thepolymer's Tg is usually lower than 120° C. because otherwise the bindercomposition may become somewhat difficult to prepare. As alreadyindicated above, the choice of the polymer's Tg can be based on the Tgrecommended for the binder composition.

If use is made of polymers having only terminal groups that can reactwith a hydroxyalkylamide functionality, the polymer has an averagefunctionality (capable of reacting with the hydroxyalkylamide groups) ofmore than 1.6, preferably more than 2. The polymer generally has anaverage functionality of less than 10, preferably less thanapproximately 6. If use is made of polymers—such as polyacrylates—withappended functional groups, the average functionality will be higherthan approximately 1.6, and preferably higher than 2. Such a polymergenerally has an average functionality of less than 8, preferably lessthan 4.

Most preferable of the suitable polymers are polyesters andpolyacrylates.

With the polymers described various properties can be obtained in thebinder and in the powder coating itself. Polyacrylates are highlyresistant to yellowing and to weather influences. The polyacrylates thatcan be used as the polymer may be based on (meth)acrylic acid,methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate,propyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,cyclohexyl(meth)acrylate, decyl(meth)acrylate, isodecyl(meth)acrylate,benzyl(meth)acrylate and hydroxyalkyl(meth)acrylates such ashydroxyethyl and hydroxypropyl(meth)acrylate and/or glycidyl esters orglycidyl ethers of alkyl(meth)acrylates.

The polyacrylates can be obtained via known processes. In theseprocesses use can be made of comonomers such as for instance styrene,maleic acid or maleic anhydride and of small amounts of ethylene,propylene and acrylonitrile. Other vinyl or alkyl monomers, such asoctene, triallyl isocyanurate and diallyl phthalate, can be added insmall amounts.

A polyacrylate containing acid groups is generally obtained throughcopolymerization of the desired amount of acid, such as for example(meth)acrylic acid, maleic acid or fumaric acid.

The polyacrylate's viscosity usually lies between 100 and 8000 dPas(measured at 158° C.; Emila).

Polyacrylates are described in the patents U.S. Pat. Nos. 3,752,870,3,787,340 and 3,758,334 and in the British patent 1,333,361, and what isdisclosed in said patents is included herein by means of this reference.

The polyurethanes that can be used as the polymer that can react withβ-hydroxyalkylamide groups include for example also the polyurethanesterminated with an acid group and a (blocked) isocyanate group.

Polyesters are usually based on the residues of aliphatic polyalcoholsand polycarboxylic acids.

The polycarboxylic acids are generally chosen from the group consistingof aromatic and cycloaliphatic polycarboxylic acids because these acidsusually have a Tg-raising effect on the polyester. In particular, use ismade of dibasic acids. Examples of polycarboxylic acids are isophthalicacid, terephthalic acid, hexahydroterepthalic acid, 2,6-naphthalenedicarboxylic acid and 4,4-oxybisbenzoic acid and, subject toavailability, their anhydrides, acid chlorides or lower alkyl esters,such as for example the dimethyl ester of naphthalene dicarboxylic acid.Although not required, the carboxylic acid component generally containsat least approximately 50 mol. %, preferably at least approximately 70mol. %, isophthalic acid and/or terephthalic acid.

Other suitable aromatic cycloaliphatic and/or acyclic polycarboxylicacids are for example 3,6-dichlorophthalic acid, tetrachlorophthalicacid, tetrahydrophthalic acid, hexahydroterephthalic acid,hexachloroendomethylene tetrahydrophthalic acid, phthalic acid, azelaicacid, sebacic acid, decanedicarboxylic acid, adipic acid, succinic acid,trimellitic acid and maleic acid. These different carboxylic acids canbe used in amounts of at most 50 mol. % of the total amount ofcarboxylic acids. These acids can be used as such or, subject toavailability, in the form of their anhydrides, acid chlorides or loweralkyl esters.

Hydroxycarboxylic acids and/or optionally lactones can also be used, forexample 12-hydroxystearic acid, hydroxypivalic acid and ε-caprolactone.If so desired, monocarboxylic acids, such as benzoic acid,tert.-butylbenzoic acid, hexahydrobenzoic acid and saturated aliphaticmonocarboxylic acids can be used in smaller amounts.

The polyalcohols, in particular diols, that can be caused to react withthe carboxylic acids to obtain the polyester include aliphatic diolssuch as for example ethylene glycol, propane-1,2-diol, propane-1,3-diol,butane-1,2-diol, butane-1,4-diol, butane-1,3-diol,2,2-dimethylpropanediol-1,3 (=neopentyl glycol), hexane-2,5-diol,hexane-1,6-diol, 2,2-bis-(4-hydroxy-cyclohexyl)-propane (hydrogenatedbisphenol-A), 1,4-dimethylolcyclohexane, diethylene glycol, dipropyleneglycol and 2,2-bis[4-2-hydroxylethoxy)-phenyl]propane and thehydroxypivalic ester of neopentyl glycol.

Small amounts, such as less than approximately 4 wt. %, but preferablyless than 2 wt. %, of trifunctional alcohols or acids can be used toobtain branched polyesters. Examples of suitable polyols and polyacidsare glycerol, hexanetriol, trimethylolethane, trimethylolpropane,tris-(2-hydroxyethyl)-isocyanurate and trimellitic acid.

Tetrafunctional monomers are usually not preferred, because they cancause excessive branching or gelling, although it is possible to usethem in very small amounts. Examples of suitable polyfunctional alcoholsand acids are sorbitol, pentaerythritol and pyromellitic acid.Trifunctional monomers are however preferred for synthesizing branchedpolyesters.

The coating properties can be influenced via for example the choice ofdiol. If for example good weather resistance is required, the alcoholcomponent preferably contains at least 70 mol. % neopentyl glycol,1,4-dimethylolhexane and/or hydrogenated bisphenol-A. Caprolactone andhydropivalic acid can also be used if good weather resistance isrequired.

The polyesters are prepared via the usual processes, throughesterification or trans-esterification, optionally in the presence ofthe usual esterification catalysts such as for example dibutyl tin oxideor tetrabutyl titanate. The preparation conditions and the COOH/OH ratiocan be chosen so that end products having an acid number or hydroxylvalue that lies within the desired range of values are obtained.

A carboxylic-acid-functional polyester is preferably prepared in aseries of steps. In the last step thereof an aromatic or, preferably,aliphatic acid is esterified so that an acid-functional polyester isobtained. As known to a person skilled in the art, terephthalic acid isin a first step caused to react in the presence of excess diol. Suchreactions result in a substantially hydroxyl-functional polyester. In asecond or subsequent step an acid-functional polyester is obtained bycausing further acid to react with the product of the first step.Further acids are for example isophthalic acid, adipic acid, succinicanhydride, 1,4-cyclohexanedicarboxylic acid and trimellitic anhydride.

Preferably trimellitic anhydride is used at a temperature of 170-200°C., because then a polyester with a relatively large number oftrimellitic acid terminal groups is obtained, as a result of which thereactivity of the binder system is increased and better coatingproperties are obtained.

The polyester may be a crystalline polyester, but amorphous polyestersare preferred. Mixtures of crystalline and amorphous polyesters can alsobe used. Amorphous polyesters have a viscosity that generally lieswithin a range from 100 to 8000 dPas (measured at 158° C., Emila).Crystalline polyesters usually have a lower viscosity in the range fromapproximately 2 to approximately 200 dPas.

If the polyester contains groups that can react with carboxylic acid,the polyester's acid number is chosen so that the desired amount ofcrosslinker can be used. The acid number is preferably higher than 10and more preferably higher than 40.

The polyester's Tg is chosen so that the Tg of the polyester-crosslinkermixture lies between for example 30° C. and 80° C., as a result of whichpowder paints or binders prepared from them are physically stable atroom temperature. Combinations of polyester and crosslinker having alower Tg can optionally be used in the preparation of a powder coatingcomposition. To retain the powder stability, such powders are howeverstored in cooled condition.

The selection of the polymer: crosslinker weight ratio depends on thedesired final application and this ratio will generally be between 60:40and 90:10, preferably between 75:25 and 85:15.

If the polymer according to the invention is used as a resin inpowder-paint compositions, compounds containing two or more functionalgroups that can react with β-hydroxyamide groups can be used as thecrosslinker. Examples of such groups are anhydrides, carboxylic acids,carboxylic esters, epoxides, isocyanates and alkoxysilanes. Preferablyanhydride groups, carboxylic acids and blocked isocyanates are used.Examples are adipic acid, decanedicarboxylic acid, trimelliticanhydride, phthalic acid or phthalic anhydride, tetrahydrophthalic acidor tetrahydro-phthalic anhydride, hexahydrophthalic acid orhexahydrophthalic anhydride and IPDI-trimer or HDI-trimer, optionallyblocked with caprolactam or triazole.

The preparation of thermosetting powder coatings in general and thechemical reactions for curing powder paints to form cured coatings aredescribed by Misev in Powder Coatings, Chemistry and Technology (1991,John Wiley) on pp. 42-54, pp. 148 and 224-226. A thermosetting bindercomposition is generally defined as the resinous part of the powderpaint consisting of polymer and crosslinker.

If so desired, the usual additives can be used in the binder compositionand in the powder-paint system according to the invention, such as forexample pigments, fillers, degassing agents, flow agents andstabilizers. Suitable pigments are for example inorganic pigments, suchas for example titanium dioxide, zinc sulphide, iron oxide and chromiumoxide, and also organic pigments such as for example azo compounds.Suitable fillers are for example metal oxides, silicates, carbonates andsulphates.

Primary and/or secondary antioxidants, UV stabilizers such as quinones,(sterically hindered) phenolic compounds, phosphonites, phosphites,thioethers and HALS compounds (hindered amine light stabilizers) can forexample be used as stabilizers.

Examples of degassing agents are benzoin and cyclohexane dimethanolbisbenzoate. The flow agents include for example polyalkylacrylates,fluorohydrocarbons and silicone fluids. Other suitable additives are forexample additives for improving tribocharging, such as stericallyhindered tertiary amines that are described in EP-B-371528.

Powder paints according to the invention can be applied in the usualmanner, for example by electrostatically spraying the powder onto anearthed substrate and curing the coating by exposing it to heat at asuitable temperature for a sufficient length of time. The applied powdercan for example be heated in a gas oven, an electric oven or with theaid of infrared radiation.

Thermosetting coatings of powder-paint (coating) compositions intendedfor industrial applications are described further in a general sense inPowder Coatings, Chemistry and Technology, Misev, pages 141-173 (1991).

Compositions according to the present invention can be used in powderpaints for use on, for example, metal, wooden and plastic substrates.Examples are industrial coatings, coatings for machines and tools,household applications and parts of buildings. The coatings are alsosuitable for use in the automotive industry for coating parts andaccessories.

DE-A-19703952 discloses a copolyester containing β-hydroxyalkylamidegroups as endgroups. The polyester polymer backbone does not compriseamide groups. The copolyester is prepared in a three step process bymixing a hydroxy polyester with a polycarboxylic acid dialkyl ester toform an alkylester group containing copolyester followed by reactionwith an aminoalcohol. In contrast, the polymer according to theinvention is a polyesteramide having amide and ester groups along thebackbone in addition to the β-hydroxyalkylamide endgroups. Thispolyesteramide results in improved mechanical coating properties by moreextensive hydrogen bridge formation, improved crosslinkdensity andimproved hydrolysis resistance.

The invention will be elucidated with reference to the following,non-limiting examples.

EXAMPLE I

Preparation of a highly branched polymer comprising units of phthalicanhydride and diisopropanolamine

384 g of phthalic anhydride and 415 g of diisopropanolamine wereintroduced into a double-walled glass reactor, which could be heated bymeans of thermal oil, fitted with a mechanical stirrer, a distillationhead and nitrogen and vacuum connections. The reaction mixture wasgradually heated, with stirring, to approx. 70° C. and then more slowlyto 170° C. A vacuum was created during the heating. The pressure in thereactor was adjusted to the release of reaction water, so that thiscould be removed from the reactor through distillation. After a totalreaction time of 6 hours the viscous polymer contained less than 0.1meq/g carboxylic acid (titrimetrically determined) and no more watercould be removed through distillation. After cooling the polymer wasobtained as a very pale yellow glassy mass. The concentration ofhydroxyl groups was titrimetrically found to be 5.4 meq/g. The numberaverage molecular mass was determined with the aid of GPC (universalcalibration) and was 1500 g/mol; the weight average molecular mass was7700 g/mol.

EXAMPLE II

Preparation of a highly branched polymer comprising units of phthalicanhydride and diisopropanolamine

232 g of phthalic anhydride and 270 g of diisopropanolamine wereintroduced into a double-walled glass reactor, which could be heated bymeans of thermal oil, fitted with a mechanical stirrer, a distillationhead and nitrogen and vacuum connections. The reaction mixture wasgradually heated, with stirring, to approx. 70° C. and then more slowlyto 170° C. A vacuum was created during the heating. The pressure in thereactor was adjusted to the release of reaction water, so that thiscould be removed from the reactor through distillation. After a totalreaction time of 5 hours the viscous polymer contained less than 0.2meq/g of carboxylic acid (titrimetrically determined) and no more watercould be removed through distillation. After cooling the polymer wasobtained as a pale yellow glassy mass. The concentration of hydroxylgroups was titrimetrically found to be 5.8 meq/g. The number averagemolecular mass was determined with the aid of GPC (universalcalibration) and was 1100 g/mol; the weight average molecular mass 4900g/mol.

EXAMPLE III

Preparation of a highly branched polymer comprising units ofhexahydrophthalic anhydride and diisopropanolamine

398 g of hexahydrophthalic anhydride and 408 g of diisopropanolaminewere introduced into a double-walled glass reactor, which could beheated by means of thermal oil, fitted with a mechanical stirrer, adistillation head and nitrogen and vacuum connections. The reactionmixture was gradually heated, with stirring, to approx. 70° C. and thenmore slowly to 160° C. A vacuum was created during the heating. Thepressure in the reactor was adjusted to the release of reaction water,so that this could be removed from the reactor by means of distillation.After a total reaction time of 3.5 hours the viscous polymer containedless than 0.2 meq/g of carboxylic acid (titrimetrically determined) andno more water could be removed through distillation. After cooling thepolymer was obtained as an almost colourless glassy mass. Theconcentration of hydroxyl groups was titrimetrically found to be 5.2meq/g. The number average molecular mass was determined with the aid ofGPC (universal calibration) and was 1550 g/mol; the weight averagemolecular was mass 7000 g/mol.

EXAMPLE IV

Preparation of a highly branched polymer comprising units ofhexahydrophthalic anhydride and diisopropanolamine

378 g of hexahydrophthalic anhydride and 436 g of diisopropanolaminewere introduced into a double-walled glass reactor, which could beheated by means of thermal oil, fitted with a mechanical stirrer, adistillation head and nitrogen and vacuum connections. The reactionmixture was gradually heated, with stirring, to approx. 70° C. and thenmore slowly to 160° C. A vacuum was created during the heating. Thepressure in the reactor was adjusted to the release of reaction water,so that this could be removed from the reactor through distillation.After a total reaction time of 5 hours the viscous polymer containedless than 0.1 meq/g carboxylic acid (titrimetrically determined) and nomore water could be removed through distillation. After cooling thepolymer was obtained as an almost colourless glassy mass. Theconcentration of hydroxyl groups was titrimetrically found to be 6.1meq/g. The number average molecular mass was determined with the aid ofGPC (universal calibration) and was 1010 g/mol; the weight averagemolecular mass 4600 g/mol.

EXAMPLES V-VIII

Powder-paint compositions comprising a polymer according to any one ofExamples I-IV

Powder-paint compositions according to Table 1 were prepared by mixingand extrusion (PRISM extruder, 120° C.). The polyesters (Uralac 5040™and Uralac 5261™ from DSM Resins) comprise units of terephthalic acid,adipic acid, neopentyl glycol and trimellitic anhydride.

The compositions were in the usual manner ground, sieved andelectrostatically sprayed (Corona) onto aluminium and steel test panels.After a cure cycle of 10 minutes at 200° C. or 15 minutes at 180° C. ina circulation oven, the panels were tested to determine their appearance(visually), flexibility (penetration in mm according to Erichsen ISO1520/DIN 53156), reverse impact resistance (ASTM-2794/69 in inch-pound),acetone resistance (acetone double rubs), adhesion (cross hatch adhesiontest) and hardness (König, seconds). The test results are shown in Table1.

These examples show that the polymers according to the invention resultin coatings having good to very good chemical, mechanical and opticalproperties and a high blister limit (visually).

TABLE 1 Compositions and coating properties Composition A B C D E FPolyester resin: Uralac 155 g 159 g 164 g P5261 ™ Uralac 156 g 162 g 160g P5040 ™ Crosslinker according to: Example I  45 g  44 g Example II  38g Example III  43 g  42 g Example IV  36 g Additives: TiO₂ 2160 100 g100 g 100 g 100 g 100 g 100 g Benzoin  3.0 g  3.0 g  3.0 g  3.0 g  3.0 g 3.0 g BYK 361  1.5 g  1.5 g  1.5 g  1.5 g  1.5 g  1.5 g cure cycle 10′10′ 10′ 15′ 15′ 15′ 200° C. 200° C. 200° C. 180° C. 180° C. 180° C.Hardness 235 s 225 s 215 s 215 s 210 s 195 s Impact >160 ip 160 ip >160ip >160 ip >160 ip >160 ip resistance¹⁾ ESP²⁾ >8 mm >8 mm >8 mm >8 mm >8mm >8 mm Adhesion³⁾ Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 Gel time⁴⁾ n.d.⁵⁾ 15180 116 85 100 Flow behaviour OK OK OK OK OK OK Blister limit 120μ 120μ130μ 140μ 140μ 140μ ¹⁾reverse impact test; on steel ASTM-2794/69. Theimpact resistance is usually given as inch × pound. If no cracks arevisible in the coating at 160 i.p., 160 i.p. is quoted as the result. Animpact resistance of 160 i.p. stands for 1.84 m.kg. ²⁾Erichsen SlowPenetration; ISO 1520/DIN 53156 ³⁾Cross-hatch adhesion; ISO 2409/DIN5315 ⁴⁾DIN 55990; part B. ⁵⁾not determined.

What is claimed is:
 1. A branched condensation polymer containing estergroups and at least one amide group in the backbone, having at least oneβ-alkyl substituted β-hydroxyalkylamide end group, having aβ-hydroxylakylamide functionality between 2 and 250 and having a weightaverage molecular mass of ≧800 g/mol.
 2. A polymer according to claim 1,wherein the polymer contains at least two groups according to formula(II):

in which

(C₁-C₂₄)(cyclo)alkyl or (C₆-C₁₀) aryl, B=(C₂-C₂₄), optionallysubstituted, aryl or (cyclo)alkyl aliphatic diradical, and R¹, R², R³,R⁴, R⁵ and R⁶ may, independently of one another, be the same ordifferent, H, (C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical.
 3. Acondensation polymer according to claim 1, wherein the polymer is apolymer according to formula (III):

in which:

(C₁-C₂₀)(cyclo)alkyl or (C₆-C₁₀)aryl,

B=(C₂-C₂₄), optionally substituted, aryl or (cyclo)alkyl aliphaticdiradical,

X²=H or X¹ and R¹, R², R³, R⁴, R⁵ and R⁶ may be H, (C₆-C₁₀) aryl or(C₁-C₈)(cyclo)alkyl radical or CH₂—OX².
 4. A condensation polymeraccording to claim 1, wherein the polymer is represented by formula(IV):

in which:

(C₁-C₂₀)(cyclo)alkyl or (C₆-C₁₀)aryl,

or OH, B=(C₂-C₂₄), optionally substituted, aryl or (cyclo)alkylaliphatic diradical,

X²=H or X¹, R³=H or (C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical, andR⁶=H or (C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical.
 5. A condensationpolymer according to claim 1, characterized in that the polymer is apolymer according to formula (V):

in which:

or OH, B=(C₂-C₁₂), optionally substituted, aryl or (cyclo)alkylaliphatic diradical,

X²=H or X¹, R³=(C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical andR⁶=(C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical.
 6. A process for thepreparation of a polymer according to claim 1, wherein, a cyclicanhydride reacts with a β-alkyl-substituted β-hydroxylalkylamine to forma hydroxylalkylamide, after which the polymer is obtained throughpolycondensation.
 7. A process for the preparation of a polymeraccording to claim 1, wherein a β-alkyl-substituted β-hydroxylalkylaminereacts with a compound containing an acid group and an activated acidgroup, after which the polymer is obtained through polycondensation. 8.A process for the preparation of a polymer according to claim 1, whereina cyclic anhydride reacts with an alcohol, after which the reactionproduct obtained reacts in situ with β-alkyl-substitutedβ-hydroxylalkylamine and the polymer is subsequently obtained throughpolycondensation.
 9. A modified polymer that is obtained through areaction between a polymer according to the formula (III) as defined inclaim 3 with a monomer, oligomer or a polymer containing reactive groupsthat react with hydroxylalkylamine.
 10. A modified polymer that isobtained through a reaction between a polymer according to the formula(IV) as defined in claim 4, with a monomer, oligomer or a polymercontaining reactive groups that react with hydroxylalkylamine.
 11. Amodified polymer that is obtained through a reaction between a polymeraccording to the formula (V) as defined in claim 5, with a monomer,oligomer or a polymer containing reactive groups that react withhydroxylalkylamine.
 12. A modified polymer according to formula (III):

in which:

(C₁-C₂₀)(cyclo)alkyl or (C₆-C₁₀)aryl,

or OH, B=(C₂-C₂₄), optionally substituted, aryl or (cyclo)alkylaliphatic diradical,

X²=H, X¹ or

in which

is derived from a monomeric, oligomeric or polymeric monofunctionalcarboxylic acid, and R¹, R², R³, R⁴, R⁵ and R⁶ may be H, (C₆-C₁₀) arylor (C₁-C₈)(cyclo)alkyl radical or CH₂—OX².
 13. A modified polymeraccording to formula (IV):

in which:

H, (C₁-C₂₀)(cyclo)alkyl or (C₆-C₁₀)aryl,

or OH, B=(C₂-C₂₄), optionally substituted, aryl or (cyclo)alkylaliphatic diradical,

R³=H or (C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical, and R⁶=H or(C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical, and X²=H, X¹ or

and in which

is derived from a monomeric, oligomeric or polymeric monofunctionalcarboxylic acid.
 14. A modified polymer according to formula (V):

in which:

or OH, B=(C₂-C₁₂), optionally substituted, aryl or (cyclo)alkylaliphatic diradical,

wherein R³=(C₆-C₁₀) aryl or (C₁-C₈)(cyclo)alkyl radical and R⁶(C₆-C₁₀)aryl or (C₁-C₈)(cyclo)alkyl radical, and X²=H, X¹ or

and in which

is derived from a monomeric, oligomeric or polymeric monofunctionalcarboxylic acid.